Hydrocarbon exploration and production typically involves using downhole tools in boreholes penetrating earth formations. These downhole tools may include multiple subs. Operation of the subs, particularly in borehole logging, may be improved by synchronization of two or more subs. The downhole conditions and tool configurations may not allow direct electrical, hydraulic, or acoustic communications between two or more of the subs. It would be advantageous to have the ability to synchronize subs under conditions where conventional downhole communications are unreliable or prevented.